Physics Flashcards
Cathode is also called the?
Filament
Anode is also called?
Target
The cathode is what charge?
Negative
The anode is what charge?
Positive.
What is the purpose of the oil in an x-ray tube?
Electric shielding X-ray attenuation/protection Transmission of heat
What percentage of the kinetic energy of the electrons colliding into the target gets converted to x-rays?
1%
What are the three main ways to cool an x-ray tube?
Brute force - add more material to the anode Material approach - Add rhenium to the focal track. Add graphite or molybdenum to the anode disk for more heat capacity. Use liquid metal vacuum bearings for faster rotation of the anode. Add circular grooves in the anode. Add more rows to reduce scan duration (indirect) Paradigm Shift - new technologies (example dual-source)
How many collimators does a CT have?
Two: Tube collimator and detector collimator
What defines the slice thickness in a single slice CT?
Tube collimator
What does a filtration do?
Filters out low-energy x-rays that contribute to patient dose and scatter
What are filters normally made from?
Aluminium ~3mm
What is the advantage of a bow-tie filter?
Allows a lot of x-rays to pass through the center of the patient and less to pass through the thinner margins of the patient.
What type of detectors are used in CT?
Scintillation detectors
What material is used in a scintillation detector?
Crystals - cesium iodide or cadmium tungstate
What is another name for the third generation gantry?
Rotate/rotate - meaning the both the x-ray tube and detectors rotate
When was CT invented?
1972
Why was fourth generation CT created?
To get rid of the ring artifact
What is the fourth generation CT?
Stationary detectors at 360 degree - very high cost
What is the collimator pitch in a single slice system?
Ratio between the table movement per 360 degrees of rotation to collimator width (single slice CT)